Should the substance contain more volatile ingredients than chlorine, the workable lead will appear of a black or dark grey color; when this occurs, it ought to be refused with the scoria for some minutes in the oxidating flame, in order to expel any sulphur or arsenic that may be present. Ores containing very small portions only of real silver present no black aspect, as the minute qualities of sulphur and arsenic are evolved on the first application of the heat.

C.

EXAMINATION OF FURNACE PRODUCTS CONSISTING OF METALLIC
OXIDES WHICH ARE EASILY REDUCIBLE UPON CHARCOAL.

The most prominent of these are the litharges and the abstrichs. If the workable lead resulting from plombiferous ores be cupellated for silver, several sorts of litharge are obtained. The first appearing immediately after the fusion of the substance, is the absung, which adheres to plombiferous minerals. The second are termed abstrichs, or black litharges, and present themselves when the molten mass is exposed to the blast; their aspect changes from black and metallic, to yellow and yellowishgrey, and they contain all the easily oxidizable metals; the metal generally predominating in them is antimony. The red litharges formed after the abstrichs, until the termination of the process, consist of nearly pure oxide of lead, contaminated only by traces of silver and oxide of copper.

Their content of silver is generally inconsiderable, and often cannot be ascertained in an assay of one decigramme. As, however, these substances consist of no foreign metal besides lead, the reduction of which is easily effected, their quantity of silver is readily determined.

Five decigrammes of the body are weighed, pulverized, and dressed with 50 milligrammes of soda, and 50 milligrammes of borax, enveloped in a cornet of soda paper, placed in a charcoal cavity, treated with the reducing flame, until all the oxide is reduced, and the scoriæ, free from lead, are perfectly liquid.

The globule obtained from the litharge is generally exempt

from volatile metals, and contains but a small proportion of copper; whereas, that obtained from the abstrich is usually contaminated with antimony, arsenic, copper, zinc, et cetera. These ingredients, however, disappear, if the scoriæ are treated for a long time with the reducing flame. The oxidation and cupellation are effected in the ordinary way. The weight of the button is determined by the scale.

d. EXAMINATION OF MINERALS WHICH ARE NOT DECOMPOSED BY BORAX OR LEAD UPON CHARCOAL.

Up to this time no mineral can be arranged under this head, except Molybdena Glance. It contains 0·176 per cent. of silver. For analyzing this mineral, the following flux has been found the most satisfactory :

Take 1 decigramme of the specimen, and dress it with—

In a cornet of soda paper inserted in a cavity in the charcoal, place the assay, and subject it to a strong reducing flame. The soda decomposes the mineral, sulphide of sodium is formed, and the liberated molybdenum partly combines with the lead, and partly volatilizes, coating the charcoal with a white sublimate. When the liquid scoria flows quietly, it is a sign that the decomposition is terminated. The argentiferous globule must now be exposed to the air, and treated with the reducing flame, until all the molybdenum, which gives a white and brittle alloy with the lead, is expelled. The addition of the borax is to prevent the recrements from dilating upon the support. The workable lead obtained is then oxidated and cupellated.

¶ B. Metallic Compounds.

a. EXAMINATION OF THOSE COMPOUNDS WHICH HAVE SILVER AS A PRINCIPAL CONSTITUENT.

Among these rank native silver, blicksilber, brandsilber, amalgamsilber, cupelled silver, and standard silver. The operation for these consists only in fusing with pure lead, and cupellating. The quantity of the substance taken may vary from 80 to 100 milligrammes, as it is very difficult to obtain a piece of a certain weight. As the examination is not effected upon exactly 100 milligrammes, a particular calculation is necessary for deducing the per centage of the assay from the weight of the treated substance; thus, 85.5 milligrammes were treated with 200 milligrammes of lead, from which 836 milligrammes of pure silver were obtained, the cupellating loss of which is 0.27 milligrammes, therefore, the following proportion is indicated:

On account of such compounds being obtained with great difficulty in small particles, as foreign matters on the surface of the sample might prevent exactness in the results, they should be scraped off previously to weighing, and treated on charcoal. If native silver, blicksilber, or brandsilber is to be assayed, one decigramme of lead and 50 milligrammes of borax are requisite, for cupriferous amalgams and standard silver; the proportion of lead varies from two to five decigrammes, however, according to the quantity of copper. The mixture is fused in the reducing flame, until the noble metal becomes alloyed with the lead, and the borax appears perfectly free from plombiferous particles. The assay is then allowed to refrigerate, and the button removed and separated from the flux. Though the addition of borax is not absolutely required, still it prevents any violent action ensuing, which, if occurring, would falsify the results.

Such alloys as require but one to two decigrammes of proof lead,

are assayed upon the cupel. Cupriferous alloys, however, treated with three to five decigrammes of lead, must first be submitted to oxidation, to dispel the greater part of the copper, and then cupelled.

The fine silver globule is, after the termination of the process, removed from the cupel, struck slightly with the hammer upon the anvil, and then weighed upon the balance.

b. EXAMINATION FOR SILVER IN METALLIC COMPOUNDS
CONSISTING CHIEFLY OF GOLD.

Under this head is placed Native Gold, and alloys consisting of gold, silver, and copper.

In these the per centage of silver is readily determined at the same time with that of gold. The procedure will be specified under the Gold Assay.

C. EXAMINATION FOR SILVER IN ALLOYS WHEREIN COPPER

AND NICKEL PREDOMINATE.

These compounds are:-black copper and gaarkupfer affined on a large scale; copper coins containing silver; brass, bellmetal, German silver, et cetera.

For procuring quantities sufficient for weighing, the alloy must be ground with a strong file, and when gaarkupfer, black copper, coined copper, or German silver is assayed, the following proportions must be employed :

The dressed sample is then wrapped in a soda paper cornet, inserted in a charcoal cavity, and treated with the reducing flame directed upon the assay, until it has been some time in fusion, and all metallic particles have disappeared from the surface. In this operation, cobalt, iron, and zinc oxidize; the first two dissolve in the borax, whereas the zinc volatilizes.

Y

The workable lead obtained, which contains copper or nickel, or both metals, may, without being cooled, be brought upon the steel anvil. This spares the detaching of the scoriæ. It is now to be cupelled in the common way, but if the globule produced contains copper, a dilation ensues, which will prevent a determination of its weight upon the scale; this is, however, remedied by adding 50 milligrammes of lead, and recupelling.

When brass or bell metal is to be assayed, the following proportions must be taken :

The assay is fused like the former, in the reducing flame, until the borax is exempt from metallic particles. The flame is then directed only upon the flux, to allow the atmospheric air access to the lead, to oxidate the tin, and the nonvolatilized portions of zinc. The oxide of tin combines with the borax ; the oxide of zinc is entirely dispelled. If, then, the surface of the assay appears bright, it must be poured upon the anvil. The subsequent operations are conducted according to the method prescribed for cupriferous substances.

d. EXAMINATION OF METALLIC COMPOUNDS, THE PREDOMINATING METALS BEING LEAD OR BISMUTH.

To this class appertain workable lead, prepared on a large scale, revivified lead, argentiferous bismuth, et cetera.

Of these alloys, the workable lead is the richest in silver; a portion is to be laminated, cut into shreds with the scissors, two decigrammes weighed out, placed upon a cupel, fused in a moderate oxidating flame, and cupelled immediately. If little or no copper is present, a bright and orbicular globule will be obtained, but when much copper is contained in the alloy, dilation ensues, without any external brightening; should this occur, one decigramme of lead ought to be added, and the operation terminated upon another part of the cupel. The weight of the button